The chromic fluoride catalysts activated by the process of this invention are useful in vapor phase halogen-exchange reactions between hydrogen fluoride and one and two carbon chlorocarbon compounds. The fluorocarbon compounds and chlorofluorocarbon compounds formed by said halogen-exchange reactions are useful, among other things, as refrigerants, aerosol propellants, solvents, and dielectric gases.
Chromic fluoride catalysts are normally packed in heated fixed-bed tower reactors through which the reactants are passed in the gas phase. In this use, the so-called activity of the catalyst, as measured by the degree of exchange of fluorine for chlorine per pass, gradually decreases until it is no longer economical to operate the column and the (spent) catalyst must be replaced. Typically, such reactors can be operated for about 750 to 1,500 hours before the catalyst must be replaced. Replacement of catalyst is expensive in terms of materials cost and lost production time.
Coassigned U.S. Pat. No. 3,855,151, discloses a method for reactivating spent chromic fluoride catalysts which comprises reacting said catalysts with a chlorine-source such as a C.sub.1 or C.sub.2 chlorocarbon capable of dissociating at reaction temperatures of 300.degree. to 500.degree. C. to produce chlorine, or, with a combination of chlorine plus a C.sub.1 or C.sub.2 chlorocarbon not capable of dissociation at such reaction temperatures. Said patent does not concern the HCl/Cl.sub.2 reaction of this invention. Art references relating to the regeneration of cracking catalysts or chromium oxyfluoride catalysts are not pertinent to the process of this invention because of the significantly different chemistry there involved.
The process of this invention has certain very desirable characteristics. For example, organic materials which are foreign to the compounds being made are not introduced by the instant process. The process is operable at atmospheric pressure but is more preferably operated at superatmospheric pressures. Operation at superatmospheric pressures makes it unnecessary to store or discard the process charge at the beginning of activation in order to return to atmospheric pressure. Instead, the charge is merely displaced through the normal recovery train by the activating chemicals. Finally, the catalyst activated according to the process of this invention has a relatively long useful life and its activity is better than would be expected by one skilled in the art.